Upper Cretaceous calcareous nannoplankton paleoecology and its biostratigraphic consequences: Western central Atlantic Ocean.

摘要

First and last occurrences of calcareous nannofossil taxa are generally thought to be synchronous across latitude and paleodepth, especially in temperate to tropical latitudes. This belief is particularly prevalent of regional studies, where stratigraphic sections examined for calcareous nannofossil content are derived from the same paleolatitude. However, even in these local studies, paleoceanographic and paleobiogeographic parameters can influence the fossil assemblage greatly, and models based on the assumption that first and last occurrences are synchronous may be incorrect. Two cores from the Blake Nose, Western Atlantic Ocean, and nine cores from the Atlantic Coastal Plain of South Carolina were examined for calcareous nannofossil content in an effort to better understand the role that paleoecology played in fossil distribution patterns.; One new calcareous nannofossil genus and four new calcareous nannofossil species are described from Upper Cretaceous sediments. The first occurrence of Micula murus, a marker species for low- to mid-latitude sites, is shown to be diachronous across the study area and its usefulness as a biostratigraphic marker for neritic sediments is questioned. The evolutionary radiation and resulting biostratigraphic utility of species of Ceratolithoides, Lithraphidites and Micula is discussed in detail and their first and last occurrences are tied to the geochronologic timescale where possible. Differences in population abundance and species richness between deep ocean and nearshore areas are shown to have been controlled by paleoceanographic factors. The investigated Maastrichtian sections are representative of similar paleolatitudes and vary significantly only in their environment of deposition. This study illustrates the difficulties of creating age models based on floral first and last occurrences calibrated from different regions and the significant role that environment can play in determining calcareous nannofossil assemblages.